Color images are generally represented in a computer environment with an independent color value for each pixel. Each color value must consist of three components in order to represent the full range of colors. Since the display monitors that are used with computers utilize RGB (red, green, and blue) as the three color components, computer images are generally represented using this color format.
Images stored in this format generally require a large data set, but also contain a lot of redundancy because of the high pixel-to-pixel correlation of typical images. If the images are part of a moving sequence of images, as in video, the storage requirements are multiplied by the number of frames. Further, the bandwidth requirements to display a video sequence are much higher than can typically be provided in a low cost computer system. It is often desirable to utilize data compression to reduce data storage and bandwidth requirements. Compression algorithms can take advantage of redundancy in the image and the peculiarities of the human vision system.
Several image compression algorithms have been developed which are reasonably effective at reducing the data storage and bandwidth requirements. The compression ratio that can be achieved is a function of the computational resources that can be applied. And since the utility of image compression is determined by the compression ratio that can be achieved, specialized VLSI compression processors are generally required to provide adequate computational resources to make image compression worthwhile. It is also necessary to provide adequate compression to reduce the bandwidth requirements of the video so that it can be stored on the available mass storage device.
The requirement for specialized VLSI has limited the market potential for digital video applications, since conventional PCs generally do not have these capabilities. To expand the market potential, a video compression method which can be implemented by conventional PCs is necessary.
Many of the applications which require video use short video clips--on the order of 10 to 15 seconds. Many personal computers will have adequate free disk space to store this much video, even with only limited compression. However, since multiple video clips are generally required for an application, a high degree of compression is ultimately required for the application to be cost effective.
Thus, an object of the invention is a method for image compression that can be executed on a conventional PC without specialized VLSI to support compression.
Another object of the invention is a compression method which will result in adequate compression to reduce the bandwidth requirements of real-time video to a level that can be supported by conventional mass storage devices as might be found in personal computers.